Cut meat across the grain into 1/2-inch strips, about 1 1/2 inches long.
Melt butter in large skillet.
Add mushrooms and onion; cook and stir until onion is tender, then remove from skillet.
In same skillet, cook meat until light brown.
Reserving 1/3 cup of the broth, stir in remaining broth, the catsup, garlic and salt.
Cover; simmer 15 minutes.
Blend reserved broth and flour; stir into meat mixture.
Add mushrooms and onion.
Heat to boiling, stirring constantly.
Boil and stir 1 minute.
Stir in sour cream; heat.